1. Field of Invention
The present invention pertains to the art of refrigerated appliances and, more particularly, to a refrigerator including a variable speed compressor that, in combination with a controller, efficiently maintains fresh food compartment temperatures within a confined temperature band.
2. Discussion of Prior Art
In general, a refrigerator includes a first or freezer compartment for maintaining foodstuffs at or below freezing, and a second or fresh food compartment, in fluid communication with the freezer compartment, for maintaining foodstuffs in a temperature zone between ambient and freezing temperatures. A typical refrigerator includes a refrigeration system having a compressor, a condenser coil, a condenser fan, an evaporator coil, and an evaporator fan.
In operation, temperature sensors are provided within the refrigerator to measure internal temperatures of the appliance. When a door associated with either compartment is opened, the temperature within the respective compartment will rise. When the internal temperature of the refrigerator deviates from a predetermined temperature, the refrigeration system is caused to operate such that the temperature will return to a point below a consumer selected set-point. In order to return the compartment temperature to this point, prior art systems are caused to operate at maximum capacity regardless of the degree of the deviation. Another consideration is the size of the temperature zone. Prior art refrigerators typically establish a wide temperature zone or bounce region in order to minimize operation of the refrigeration system. A small temperature zone or bounce region results in extended operation of the system, thereby reducing energy efficiency.
A supplement to compressor operation is the addition of a variable position damper located between an evaporator housing and the fresh food compartment. Operation of the damper is controlled such that cool air is permitted to flow from the evaporator to the fresh food compartment. In some arrangements, a fan is mounted within a housing adjacent to the evaporator to aid in establishing the air flow. Accordingly, if the temperature of the fresh food compartment rises above the set-point, the damper is operated to allow the passage of cooling air from the evaporator compartment to the fresh food compartment. Unfortunately, this results in operation of the compressor each time additional cooling air is required.
Earlier systems require running the refrigeration system at its maximum level in order to lower the temperatures in the compartments. As time progressed, systems were developed which varied the speed of one or another of the individual refrigeration components, e.g. the compressor, the condenser fan, and/or evaporator fan, depending upon the magnitude of the temperature deviation. Additionally, a fan is incorporated into a chamber adjacent to the fresh food compartment to recirculate air within the compartment in order to reduce temperature stratification.
While these systems work to improve refrigeration efficiency, they have never been fully integrated so as to obtain a synergistic benefit, with each component being operated in a manner to maximize the efficiency of the refrigerated appliance. Nor are the various components designed to be operated by a control system specifically designed to determine the energy maximizing speed for the compressor based on predicted temperature values, the rate of temperature change in each of the fresh food and freezer compartments and the overall system design. Accordingly, there exists a need for a refrigeration system which varies the speed of the compressor based on a method of control such that maximum efficiency is achieved.
A refrigerator constructed in accordance with the present invention is energy efficient, having a reduced noise output and minimal thermal stratification. In addition to the typical components found in a refrigerator, e.g. an insulated cabinet shell having a fresh food compartment and a freezer compartment, shelves for supporting food items, and in some arrangements drawers for storing fruit, vegetables and meats, the refrigerator of the present invention includes an electronic control system capable of operating a refrigeration system for maintaining one or more of the compartments at a substantially constant temperature with minimal energy input.
To this end, the refrigerator of the present invention includes a variable speed compressor, an evaporator fan, and a fresh food stirring fan. Additionally, a multi-position damper is located within a duct connecting the fresh food and freezer compartments for controlling a flow of cooling air between the two compartments. The refrigeration components are interconnected to the electronic control system which receives signals from a plurality of sensors and functions to vary the speed of the compressor such that the refrigeration system operates to maintain the temperature of the compartments with minimum compartment temperature variations and, in the case of fresh food compartment, within a confined temperature band.
During normal usage, the refrigerator will be accessed several times a day through the opening and closing of at least one compartment door. This opening and closing results in a rise in an internal temperature of the appliance. Furthermore, the addition of various loads, i.e. foodstuffs into each of the compartments will also increase compartment temperature. When internal compartment temperatures exceed a predetermined limit, sensors send a signal representative of that temperature change to the electronic control system. Based upon the magnitude and direction of the temperature change, the electronic control system determines not only which component(s) require activation, but also the optimum speed at which the compressor should be operated. Therefore, for example, a low cooling demand results in a low speed operation, a medium cooling requirement results in a medium speed operation, etc. However, the operation of the components are interdependent such that temperature control is performed in a synergistic manner. For instance, the operational speed of the compressor is established based on sensed temperatures in the freezer and fresh food compartments, the rate of change of the temperature in the freezer compartment, the rate of change of the freezer compartment temperature relative to a set point, the rate of change of the temperature in the fresh food compartment, the rate of change of the fresh food compartment relative to a set point and, if so equipped, a set point temperature of one or more high performance specialty compartments.
Based on the above, it is the manner in which the electronic control varies the operational speed of the compressor based on estimated and sensed temperature conditions in order to maximize operational efficiency to which the invention is directed. In any event, additional objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment of the invention when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.